JetOSSnapshotPrepare Function

Article
08/26/2021

Applies to: Windows | Windows Server

JetOSSnapshotPrepare Function

The JetOSSnapshotPrepare function begins the preparations for a snapshot session. A snapshot session is a short time interval in which the engine does not issue any write IOs to disk, so that the engine can participate in a volume snapshot session (when driven by a snapshot writer).

Windows XP: JetOSSnapshotPrepare is introduced in Windows XP.

    JET_ERR JET_API JetOSSnapshotPrepare(
      __out         JET_OSSNAPID* psnapId,
      __in          const JET_GRBIT grbit
    );

Parameters

psnapId

The identifier of the snapshot session to be started.

grbit

The options for this call. This parameter can have a combination of the following values.

Value	Meaning
0	Normal snapshot.
JET_bitIncrementalSnapshot	Only log files will be taken.
JET_bitCopySnapshot	A copy snapshot (normal or incremental) with no log truncation.
JET_bitContinueAfterThaw	The snapshot session occurs after JetOSSnapshotThaw and will require a JetOSSnapshotEnd function call.
JET_bitExplicitPrepare	No instances will be prepared by default. Windows 7: JET_bitExplicitPrepare is introduced in Windows 7.

Return Value

This function returns the JET_ERR datatype with one of the following return codes. For more information about the possible ESE errors, see Extensible Storage Engine Errors and Error Handling Parameters.

Return code	Description
JET_errSuccess	The operation completed successfully.
JET_errInvalidParameter	The snapshot ID pointer is NULL or the grbit parameter is invalid.
JET_errOSSnapshotInvalidSequence	A snapshot session is already in progress and the operation is not allowed to have more than one snapshot session at any given time.

If this function succeeds, a snapshot session will be able to start at any time with the IO freeze phase. The identifier for the session will be returned and must be used in the subsequent calls for the snapshot session.

The running instances of the engine will now be considered part of the snapshot session.

Windows Vista: To specify a different subset of instances, the JetOSSnapshotPrepareInstance can be called.

The normal API sequence call is: JetOSSnapshotPrepare, optionally followed by one or more calls to JetOSSnapshotPrepareInstance, then followed by JetOSSnapshotFreeze. Once the freeze is started, it can be terminated using JetOSSnapshotThaw. At any time after the prepare, the snapshot session can be abruptly terminated with JetOSSnapshotAbort.

If JET_bitContinueAfterThaw is specified after JetOSSnapshotThaw, the snapshot session will remain (although the I/O will resume). This will enable a verification of the snapshot, and if needed, will enable log truncation using JetOSSnapshotTruncateLog and will require a call to JetOSSnapshotEnd.

If this function fails, no change in the engine state occurs.

Remarks

Event log entries will be generated for the different steps of the snapshot.

Requirements

Requirement	Value
Client	Requires Windows Vista or Windows XP.
Server	Requires Windows Server 2008 or Windows Server 2003.
Header	Declared in Esent.h.
Library	Use ESENT.lib.
DLL	Requires ESENT.dll.

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JetOSSnapshotPrepare Function